The present invention relates to an improved ink composition for ink jet recording, which is used for an ink jet recording apparatus for performing recording by jetting ink drops in response to electric signals to cause the ink to adhere onto a recording medium.
In order for an ink for ink jet recording to be jetted in drops stably at high speeds, the ink should have the following properties at temperatures approximating room temperature:
(1) Viscosity: lower than 5 cps PA0 (2) Surface tension: 40-50 dyne/cm PA0 (3) Amount of dissolved air: less than about 0.013 ml/ml
Inks disclosed in the specifications of U.S. Pat. No. 3,846,141 and British Pat. No. 1,378,894 satisfy the requirements for the viscosity and surface tension among the above three requirements. Namely, in an ink comprising water, a water-soluble wetting agent and a water-soluble dye, an ink comprising a water-soluble solvent in addition to the foregoing basic components and an ink further comprising a minute amount of a surface active agent, it is possible to reduce the viscosity below 5 cps and adjust the surface tension to 40-50 dyne/cm. However, in conventional ink compositions for ink jet recording, no adjustment of the amount of dissolved air is made. If the amount of dissolved air is too large, increase of the pressure for jetting cannot be precisely transferred through the ink, and therefore, it becomes difficult to perform recording precisely in response to electric signals.